CVE-2019-1166 in Windows
Summary
by MITRE
A tampering vulnerability exists in Microsoft Windows when a man-in-the-middle attacker is able to successfully bypass the NTLM MIC (Message Integrity Check) protection, aka 'Windows NTLM Tampering Vulnerability'.
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Analysis
by VulDB Data Team • 09/26/2020
The Windows NTLM tampering vulnerability represents a critical security flaw that undermines the integrity protection mechanisms of the NTLM authentication protocol. This vulnerability specifically targets the Message Integrity Check component of NTLM, which is designed to prevent message modification during authentication exchanges. When successfully exploited, the vulnerability allows attackers to manipulate authentication messages without detection, effectively bypassing the security controls that should protect against tampering. The issue resides within the Windows operating system's implementation of the NTLM protocol, making it a systemic weakness that affects all affected versions of the platform.
The technical exploitation of this vulnerability occurs through man-in-the-middle attacks where an attacker intercepts and modifies NTLM authentication messages. The NTLM MIC field, which should validate that messages have not been altered during transmission, becomes ineffective when the vulnerability is present. Attackers can manipulate the authentication flow by removing or modifying specific fields in the NTLM message sequence, allowing them to establish unauthorized connections or escalate privileges. This flaw specifically impacts the authentication process where the MIC field fails to properly validate message integrity, enabling attackers to forge authentication responses that would otherwise be rejected by proper validation mechanisms.
The operational impact of this vulnerability extends beyond simple authentication bypasses to encompass significant security implications for enterprise environments. Organizations relying on NTLM authentication for internal network access, file sharing, and service connections face potential unauthorized access to sensitive resources. The vulnerability particularly affects systems that depend on NTLM for legacy applications and services, creating opportunities for attackers to escalate privileges or gain persistent access to network resources. This weakness undermines the fundamental security assumptions of NTLM-based authentication systems and can facilitate lateral movement within networks where NTLM is still in use.
Mitigation strategies for this vulnerability require immediate implementation of security patches from Microsoft, which address the underlying NTLM MIC validation issues. Organizations should also consider disabling NTLM authentication where possible and implementing stronger authentication protocols such as Kerberos or modern authentication methods. Network segmentation and monitoring solutions can help detect anomalous authentication patterns that might indicate exploitation attempts. The vulnerability aligns with CWE-310, which covers cryptographic issues related to message integrity checks, and maps to ATT&CK technique T1075, which addresses credentials from password hashes. Security teams must also implement proper network monitoring to detect man-in-the-middle activities and ensure that all systems receive timely security updates to prevent exploitation of this critical authentication weakness.